For 24 years Davies lived in a common law relationship with Vancouver city councilor Bruce Eriksen,[7] who died of cancer in 1997.[8] They had a son, Lief. In 2001, Davies became the first female Canadian Member of Parliament to reveal that she was in a same-sex relationship.[5][9]

Davies was first elected to parliament in 1997 and re-elected in 2000, 2004, 2006 and 2008 and 2011. Previously the NDP House Leader and spokesperson for housing, homelessness and multiculturalism, she became Health Critic in the shadow cabinet of Jack Layton upon the NDP's ascent to Official Opposition status. In parliament she has been a strong supporter of drug policy reform, specifically to halt the criminalization of drug users.

In 2005, during the parliamentary debate on same-sex marriage in Canada, Conservative MP Jason Kenney cited Davies' prior relationship with Eriksen as proof that marriage law doesn't discriminate against LGBT individuals, since a gay person can marry a member of the opposite sex. Davies, who was never formally married to Eriksen, joined other commentators in criticizing Kenney for playing politics with other parliamentarians' personal lives.

Davies faced accusations of anti-semitism stemming from a June 5, 2010, interview in which she suggested that Israel has been occupied territory since 1948. She was criticized for her comments the next day in an Ottawa Citizen editorial. She responded to these criticisms in a letter to the Citizen, which was also posted on Davies' constituency website.[12]